Why not "They have gotten used to each other"
Yeah, that should be accepted. There's essentially no difference between those in Swahili.
I gave the exact same answer (in June 2020, two years later) and it is still not accepted. For what it's worth, I think it's the more accurate translation of this Swahili phrase.
When is used ME-tense and when NA-tense in swahili? Why not wanazoeana?
I think that kuzoea is something like get used to. If you use the present -na- you indicate the inchoative: they are getting used. You need -ma- to indicate the result: they have gotten used to, so they are used to. But I am not an expert.
Thanks for comment.